The rapid development of mobile information terminals such as cellphones, laptops, and smartphones into smaller and lighter ones in recent years has led to the demand for higher-capacity batteries as power supplies for driving them. Lithium-ion batteries, which charge and discharge through the movement of lithium ions between positive and negative electrodes, are widely used as power supplies to drive such mobile information terminals because of their high energy density and high capacity.
The above mobile information terminals are going to be higher power consumption due to their advanced video playback, gaming, and other features, leading to strong demand for higher capacities. Examples of measures to increase the capacity of a nonaqueous electrolyte secondary battery include increasing the capacity of the active material and increasing the quantity of the active material per unit area. Another way is to increase the charge voltage of the battery, but increasing the charge voltage of a battery disadvantageously makes the electrolyte more decomposable. In particular, storage or repeated charge-discharge cycles of such a battery at high temperatures affects the discharge capacity.
As a solution to this, PTL 1, for example, proposes allowing the presence of a group-3 element on the surface of particles that provide a matrix for the positive electrode active material to reduce the damage to charged storage characteristics associated with the decomposition reaction of the electrolyte that occurs at the boundary between the positive electrode active material and the electrolyte when the charge voltage is increased.
This technology disclosed in PTL 1, however, did not produce sufficient low-temperature discharge performance, although the publication mentions it reduces damage to charged storage characteristics.